The present invention relates generally to a method of engine compression release braking, and more particularly to a reduced noise method of engine compression release braking.
For a typical four stroke diesel engine, reciprocation of a movable piston between its top dead center and bottom dead center positions correspond to four stages of the engine""s operation. When the piston retracts from top dead center for the first time, it is undergoing an intake stroke, and air can be drawn into the cylinder, typically via an intake valve. When the piston advances from bottom dead center for the first time, it is undergoing a compression stroke, and air within the cylinder can be compressed. At some point during the compression stroke, relatively late for traditional diesel engines and relatively early for homogeneous charge compression engines, fuel is injected into the cylinder. At the end of the compression stroke, combustion occurs within the cylinder and the piston is driven toward bottom dead center for a power stroke. Finally, as the piston advances toward top dead center, it undergoes an exhaust stroke, and post combustion products can be removed from the cylinder, typically via an exhaust valve. While this is the typical operation for a four cycle diesel engine, it is known in the art that injection and combustion are not always desirable during each engine cycle. A number of engine operating strategies have been developed in which engine braking, rather than injection and combustion, can occur during the engine cycle. In these engine operating strategies, the exhaust valve is opened at least once prior to the exhaust stroke to release energy within the cylinder, thus producing a retarding torque on the engine.
One braking strategy is commonly referred to as the single lift engine braking method. For this engine operating strategy, the exhaust valve is opened only one time prior to the exhaust stroke, when the cylinder piston is at or near top dead center for its compression stroke. While there are a number methods for carrying out the single lift strategy, one example of this engine braking strategy is disclosed in U.S. Pat. No. 5,586,531, which issued to Vittorio on Dec. 24, 1996. Vittorio discloses a single lift engine braking method in which the engine cylinder is opened to the exhaust manifold relatively early during the compression stroke, as opposed to later in the stroke when the cylinder piston is at or near its top dead center position. Depending on the structure of the engine brake, e.g. cams and or electrically controlled actuators, the breaking event can occur every, or every other, stroke of the piston from BDC to TDC. Single event engine braking is relatively noisy when cylinder blow down occurs near top dead center.
In addition to these single lift strategies, and in an effort to gain even more engine braking horsepower, a boosted dual lift strategy has been developed. Such a strategy is described in co-owned U.S. Pat. No. 5,724,939. For this engine braking strategy, the exhaust valve is opened two times prior to the exhaust stroke of the cylinder piston. First, the exhaust valve is opened near the end of the intake stroke of the cylinder piston to allow a small amount of additional air flow into the cylinder from the exhaust manifold. Then, the exhaust valve is re-opened near the end of the compression stroke to blow down compressed air for engine braking purposes. By introducing additional air from the exhaust manifold into the cylinder at the end of the intake stroke, the amount of air in the cylinder and the cylinder pressure that results from compression can be increased, thus leading to an increased amount of engine braking horsepower that is produced. While these strategies have shown promise in increasing braking horsepower, the side effect is increased noise.
The present invention is directed toward overcoming one or more of the problems set forth above.
In one aspect of the present invention, a method of engine compression release braking includes a step of opening an exhaust manifold to an engine cylinder during a portion of an intake stroke when exhaust manifold pressure is peaking. Gas in the engine cylinder is then compressed. The engine cylinder is opened to the exhaust manifold when cylinder pressure exceeds exhaust manifold pressure.
In another aspect of the present invention, a method of engine compression release braking includes a step of opening an exhaust manifold to an engine cylinder during a substantial portion of an intake stroke while an intake valve is open. Gas in the engine cylinder is then compressed. The engine cylinder is opened to the exhaust manifold when cylinder pressure exceeds exhaust manifold pressure.
In yet another aspect of the present invention, a method of engine compression release braking includes a step of opening an exhaust manifold to an engine cylinder when a cylinder piston is in a middle region between a top dead center position and a bottom dead center position. Gas in the engine cylinder is then compressed. The engine cylinder is opened to the exhaust manifold when cylinder pressure exceeds exhaust manifold pressure.